Means and method of heating fluid



April 10, 1934. A MEKLER 1,954,089

MEANS AND METHOD OF HEATING FLUID FiledAug. 11,1930 zsneets-sneen 1 o @@C? f Win16/ ff,

April 10, 1934. A, MEKLER 1,954,089

MEANS AND METHOD OF HEATING FLUID Filed Aug. 11, 1930 2 Sheets-Sheet 2 a w1 l@ i 'i kl/N 5 1% E /m Patented Apr-.'10, 1934 UNITED STATES vPATENT OFFICE MEANS AND METHOD 0F HEATING FLUID Lev A. Mekler, Chicago, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a corporation of South Dakota .Application August 11, 1930, serial No. 474,634

6 Claims.

ploying a combination of radiant and convection heating banks of tubes and embodies the principle of partially cooling the fresh combustion products first by indirect contact with recirculated combustion gases, then by contact with the convection heating surfaces, simultaneously recirculating and reheating a portion of the cooled combustion products having passed through a portion of the convection heat section. By this method I am able to maintain a low temperature differential between the fresh combustion products and the combustion products leaving the furnace or, more particularly, I am able to maintain a low temperature differential between the top and bottom of the convection heat section.

Wide variations in the rate of heat input into the different portionsof the heating coil are possible with the heating methods and furnace structure herein disclosed and, by variations in the flow of oil through the various portions of the heating element, substantially any desired heating curve may be obtained. These features will be more fully explained hereinafter and, together with other important features, will be apparent upon reference to the accompanying drawings which, while not to scale, will serve to illustrate diagrammatically one of the many forms of furnace structure which may be utilized in the practice of the present invention.

In the drawings, Fig. 1 illustrates a sectional elevation through the furnace taken on the line 1--1 in Fig. 4.

Fig. 2 is a detail perspective View of a portion of one of the combustion tunnels showing particularly a preferred form of recirculating duct.

Fig. 3 is a detailed perspective view of another form of combustion tunnel and recirculating ducts.

Fig. 4 is a sectional plan view of the furnace taken on the line 4-4 in Fig. 1.

Figs. 5, 6 and 7 illustrate schematically three of the Various flows, which may be employed, through the different sections of the heating element.

Referring in detail to the drawings and particularly to Figs. 1, 2 and 3; 2 comprises the side walls and 4 the roof of the furnace, 5 is the fioor of the furnace and 27 is a flue leading to a stack, not shown. The walls, roof and floor of the furnace may take any of the well known forms; for instance, walls 2 may be constructed of one or more courses of firebrick inside, backed by one or more courses of common brick on the outside with an air space therebetween, and roof 4 may -be of the suspended or fiat arch type supported by structural members, not shown in the drawings. An arched roof and solid walls or any other suitable type of construction may, however, be employed if desired. Burners 6 may be may preferably be fired from both ends of each y of the two ring tunnels 7.

Firing tunnels '7, as shown more clearly in Fig. 2, are a. double-wall structure, 9 being the inner walls and 10 the outer walls. Relatively cool gases enter the duct 8, formed between walls 9 and 10, along the opening 17V next to the convection heating bank, are heated by conduction through and radiation from these heated walls, ris through the ducts 8 due to the heat imparted to these gases and their consequent decreasing density and pass from the ducts 8 back to the furnace above the convection heating bank through openings 18.

The heating element, as here shown, may comprise a plurality of elongated tubes which are preferably serially connected at their ends by return headers, not shown. At 12 is showna roof bank of radiant heat tubes comprising a shielded or upper row 13 and exposed or lower row 14, and 15 is a convection heat bank of which the lower three or four rows, more or less, designated as 16 may be a preheating or soaking section.

The combustion products from tunnel 'I are deflected away from'radiant heating element 12 by the shape of ducts 8 toward the middle of the furnace and the convection heat bank 15.

These combustion gases are first partially cooled by contact with the walls of elements 8 through which the recirculated gases are heated by conduction through and radiation from these walls and then by radiation to the relatively cool radiant heat tubes carrying relatively cool fluid. The partially cooled gases thence pass down through the convection bank l5 and out to the stack through flue 27. A portion of the gases passing through convection bank 15 is diverted through the recirculating and reheating ducts 8,

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where the gases are reheated by heat generated by the burners 6, transmitted by radiation from and conduction through the walls of ducts 8. This recirculation is thermally induced by the difference in temperature between the walls of the recirculating ducts 8 and the ue gases passing through the convection bank 15. Gases to be recirculated enter the ducts 8 at points 17, following the course indicated by the arrows, and emerge at points 18 above the convection bank of tubes.

By virtue of the reheating thus obtained by recirculation of the cooled gases through the ducts 8 and by virtue of the cooling action imparted to the fresh combustion gases by radiation to the relatively cool surfaces of the radiant heat section, milder furnace temperatures may be obtained than would be otherwise possible with the same heat input and a low temperature dierential may be obtained between the gases above and at the bottom of the convection heat section so that the lower portion of this section is more effective than would otherwise be the case.

Fig. 3 illustrates another form of recirculating ducts which may be utilized. Firing tunnels 7', as here shown, corresponding to tunnels 7 in Fig. 2, are formed of a plurality of recirculating ducts 8' spaced apart by front wall 9' and rear Wall 10'. Deecting plates 11 are provided to deflect the flame and fresh combustion products emitted from firing tunnels 7 away from the side walls 2 of the furnace and the radiant heat bank 12 toward the mid-portion of the furnace. The elements enclosing firing tunnel 7', namely the recirculating ducts 8', front wall 9', rear wall 10'` and deflector 11, as well as the corresponding elements comprising firing tunnel '7, may be constructed of refractory material, of radiating material such as silicon carbide, fused alumina or of metallic alloys which do not deteriorate at high temperatures, such as Ascoloy as well as other non-ferrous and ferrous alloys.

Fig. 5 diagrammatically illustrates one path of flow through the various portions of the heating element. This flow may be employed when a long soaking period is desired for the products to be heated. The material to be heated may be introduced into the preheating bank 16, thence passing through line 19 to the exposed row 14 and back through the shielded row 13 of the radiant heat tube bank 12, thence through line 20 to and through the convection section 15 of the heating element, parallel to the flow of furnace gases, and out through line 21.

Fig. 6 diagrammatically illustrates another flow which may be employed if a comparatively short soaking period is desired. The material to be heated enters the preheating bank 16, passes up through line 22 to and through the shielded row 13 and back through the exposed row 14 of radiant heat tube bank 12, down through line 23, upwardly through the convection bank 15, countercurrent to the iiow of combustion gases, and out through line 24.

Fig. 7 illustrates another flow which may be employed when little or no soaking time is desired in the heating element. heated is introduced into the lower portion of convection heat'bank 15 (no separate preheating section being employed in this case), through line 25 to the shielded row 13 and back through the exposed row 14 of radiant heat tube bank 12, down through line 26 into the upper section 15a of convection bank 15 at a point several rows down from the top of this bank, upward through The material to be l these several rows countercurrent to the liiow of combustion gases and out through line 24.

The improved furnace provided by my invention permits a wide variation in the rates of heat input into the different portions of the heating element. These variations may be obtained by permissible variations in the methods of firing or by variations in the flow through the different portions of the heating element or by both of these. For example, by increasing the percentage of excess air introduced into the combustion tunnels a lower temperature may be obtained in the combustion tunnels and consequently less heat may be transmitted to the gases being recirculated through the ducts 8.

'Ihe present invention permits the Widest variation in operating iiexibility resulting from the use of varying quantities of excess air over the theoretical, for example, by varying the quantity of excess air from a minimum of 10 25% over the theoretical to a maximum 20G-300% excess over the theoretical a greater or smaller rate of heat input can be accomplished into the radiant tube bank 12 and the upper portion of the convection bank 15.

As further examples of the advantages of my invention the present improvement has all of the advantages of a flue gas recirculating furnace without the necessity of using a flue gas recirculating fan, which eliminates the operating difculties and costs connected with the latter. The refractories and heating tubes of the furnace, are not subjected to the intense heat prevailing in the .usual open fired radiant and convection heat furnaces.

Recirculated products of combustion do not enter the combustion zone and therefore do not act as diluents of the atmosphere in the combustion zone permitting very good combustion with small quantities of excess air.

The recirculated gases are reheated before mixing with the products of combustion thus preventing zones of uneven temperature in the furnace.

The rate of heating of the oil either in distillation and/or cracking operations may remain practically constant with different rates of firing and throughput as increased firing automatically increases the thermal circulation vof the gases through the recirculating ducts.

It will be understood that the above examples are purely illustrative of the flexibility of operating conditions which it is possible to maintain in this type of furnace and are not intended as a limitation thereon.

I claim as my invention:

1. In the operation of furnaces wherein spent combustion gases are recirculated through the furnace in admixture with freshly generated combustion gases, the improvement which comprises thermally inducing the recirculation of the spent combustion gases through the furnace by temperature difference and indirect heat exchange between the spent combustion gases and the freshly generated combustion gases.

2. In the heating of materials in furnaces whereinv cooled combustion gases discharging from the furnace are recirculated through the furnace, the method which comprises first generating hot combustion gases and cooling the same by indirect heat exchange with the cooled combustion gases being recirculated, utilizing thel temperature difference between said hot combustion gases and said cooled combustion gases to thermally induce the recirculation of the latter.

3. In a furnace, the combination of means for generating hot combustion gases, means for recirculating spent combustion gases through the furnace, and means for thermally inducing such recirculation by the temperature difference betweenfsaid hot combustion gases and said spent combustion gases.

4. In combination with a furnace, a substantially U-shaped double-walled structure, means for generating hot combustion gases within said structure, means for circulating cooled combustion gases discharging from the furnace between the walls of said structure, means for containing material to be heated, and means for passing the first-mentioned gases and the second-mentioned gases in admixture over the containing means.

5. In the operation of furnaces wherein cool combustion gases discharging from the furnace are recirculated through the furnace, the method which comprises generating hot combustion gases in indirect heat exchange with the cool combustion gases being recirculated thereby cooling the freshly generated gases and heating the cool gases, then mixing the thus cooled freshly generated gases with the recirculated gases, and passing the resultant mixture in heat exchange with an element to be heated, and utilizing the temperature difference between said hot combustion gases`V and said cool combustion gases to thermally induce the recirculation of the latter.

6. In the operation of furnaces wherein cool combustion gases discharging from the furnace are recirculated through the furnace, the method which comprises generating hot combustion gases in a combustion zone within the furnace, passing the cool combustion gases being recirculated contiguous to said combustion zone and in indirect heat exchange with the gases being generated, then mixing the freshly generated gases with the recirculated gases, and passing the resultant mixture in heat exchange with an element to be heated, and utilizing the temperature diierence between said hot combustion gases and said cool combustion gases to thermally induce the recirculation of the latter.

LEV A. MlEKLER. 

